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Fire Opal

Opal

By Tim Matthews, JD, FGA, GG, DGA,
CEO and President of JTV
Published: June 2014
Modified: October 2022
Fire Opal Polished Fire Opal Rough Fire Opal Jewelry
Table of Contents
  • General Information
  • Fire Opal Colors
  • Fire Opal Spectra
  • Alternate Names
  • Countries of Origin
  • Care
  • Creation Method
  • Optical Phenomena
  • Related Videos

Fire opal is the name given to a variety of opal found in North, Central, and South America that is yellowish to reddish. The most valuable material is transparent and reddish. Red varieties are often called cherry opal. Sun opal is a trade name applied to a bright yellow variety of Mexican fire opal. Fire opal commonly exhibits greenish to greenish brown fluorescence. It typically does not display play-of-color phenomena but occasionally fine examples with play-of-color will occur. The more notable sources are Brazil, Guatemala, and Mexico.

General Information

  • Classification
  • Optical Properties
  • Characteristic Physical Properties
  • Chemistry & Crystallography
Common Name
Fire Opal
Species
Opal
Transparency
Transparent - Opaque
Refractive Index
1.370-1.460 Tolerance: (+0.020/-0.080) Typical 1.42-1.43
Optic Character
NA
Polariscope Reaction
Singly Refractive (SR) With ADR
Fluorescence
SWUV: Inert to moderate greenish brown
LWUV: Inert to moderate greenish brown
Pleochroism
None
Hardness
5-6.5
Streak
White
Specific Gravity
1.920-2.38 Typical:2.150
Toughness
Varies
Inclusions
Fire opal might have a cloudy appearance, show color zoning, and have mineral, fluid, and flake-like inclusions. Occasionally pyrite and dendritic inclusions.
Luster
Vitreous, Resinous
Fracture
Conchoidal, Uneven
Cleavage
None
Chemical Name
hydrated silicon dioxide
Chemical Formula
SiO2.nH2O
Crystal System
NA
Chemistry Classification
Silicate

Fire Opal Colors

  • Orange Fire Opal
    Orange
  • Yellow Fire Opal
    Yellow
  • Red Fire Opal
    Red
  • Orange Fire Opal
    Orange

Fire Opal Spectra

Fire Opal Spectra
FIRE OPAL

Color due to internal structure. Like most fire opals there is very little transmission in the violet blue side of the visible spectrum. In the lighter colored stones as here, absorption sets in about 540nm. but in the darker specimens only red and orange may be transmitted.

We acknowledge the significant scientific contributions of John S Harris, FGA to the study of gemstone spectra and with deep appreciation to him, acknowledges the use of his images and related notes about gemstones and their spectra in the educational materials on this website.

Alternate Names

Precious Opal, Mexican Fire Opal, Brazilian Fire Opal, Cherry Opal, Gold Opal, Sun Opal

Countries of Origin

Tanzania, United Republic Of; Ecuador; Argentina; Russian Federation; Hungary; United States of America; Madagascar; Kazakhstan; United Kingdom of Great Britain and Northern Ireland; Bolivia (Plurinational State of); Canada; Austria; Turkey; Unknown; Brazil; Honduras; Mexico; Slovakia; Australia; Ethiopia; Indonesia

Care

Avoid water, heat and solvents. Fire Opal is moderately soft, so be mindful of scratching.

Creation Method

Synthetic Fire Opal

Synthetic Fire Opal was manufactured by Rhea Industries and marketed as “Mexifire®”. The material was first reported in the scientific literature in 2008 and has been modified throughout the years to improve the product currently in the marketplace.

Synthetic Fire Opal Fire Opal
Synthetic Fire Opal Fire Opal
  • Classification
  • Characteristic Physical properties
Common Name
Synthetic Fire Opal
Specific Gravity
1.63
Toughness
Fair
Inclusions
Pinpoint inclusions and zoned turbidity

Optical Phenomena

Cat's Eye Fire Opal

Cat's Eye Fire Opal Fire Opal
Cat's Eye Fire Opal Fire Opal
  • Classification
Common Name
Cat's Eye Fire Opal

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